A conventional vehicle braking device includes a master cylinder, an output piston that is driven by a force corresponding to fluid pressure in a servo chamber to change the capacity of a master chamber, an input piston that defines a first fluid pressure chamber filled with brake fluid between the input piston and the output piston, the input piston cooperating with a braking operation member, a mechanical servo pressure generation unit that outputs a fluid pressure corresponding to fluid pressure inputted to a pilot chamber to the servo chamber, and a pilot pressure generation unit that generates a fluid pressure corresponding to an inputted control signal to the pilot chamber. Such vehicle braking device is described in Japanese Unexamined Patent Publication No. 2011-240873.
As an example of the mechanical servo pressure generation unit, a mechanical regulator that generates a fluid pressure corresponding to a pilot pressure in a servo chamber based on an accumulator pressure in an accumulator is described in Japanese Unexamined Patent Publication No. 2013-193619.
As described above, some vehicle braking devices include the pressure adjustment unit that outputs the output pressure corresponding to the pilot pressure inputted to the pilot chamber to the servo chamber. Basically, the pressure adjustment unit includes a piston driven by a difference between a force corresponding to the pilot pressure and a force corresponding to the output pressure, and the capacity of the pilot chamber changes with movement of the piston.